US Airways

NPRM 2007-NM-256-AD paragraph (g) proposed to mandate certain inspection, repair/overhaul, installation(s), and corrective actions to the 737 Horizontal Stabilizer Trim Actuator (HSTA) in accordance with Service Bulletin (SB) 737-27A1277 (NG) and SB 737-27A1278 (CL). Said NPRM paragraph (i) further prohibit installation of, after AD effective date, any HSTA without first complying with applicable requirements in paragraph (g). We respectfully submit two comments for your considerations. "INSTALLATION"/MODIFICATION NPRM paragraphs (g) and (g)(1)(ii)(C) referred to the term "installation(s)". We infer FAA was referring to many references in said Service Bulletins about removing certain parts and installing improved parts per vendor service bulletins. We believe using the term "installation(s)" in this context might be confusing and such actions would be better referred to as "modification(s)". Installation could refer to installation of modification Service Bulletins or installation of the HSTA unit thus making the mandate unclear. COMPLIANCE TIME NPRM paragraph (g)(1) gave compliance time as that defined in the compliance section of said SBs or that defined in the NPRM whichever comes later. Table 1 on page 35 of the compliance section in SB 737-27A1278 for the CL required modifications within 24,000 (K) hours since delivery or 24K hours since last overhaul. Header of the that Table further specified whichever comes first. The SB compliance requirement effectively made all HSTA having more than 24K hours since delivery out of compliance immediately as that would be what come first. That statement in SB Table 1 when coupled with NPRM paragraph (g)(1)(ii)(C) would give operators only twelve months to modify all affected units. Table 1 on page 42 of the compliance section in SB 737-27A1277 for the NG, on the other hand, required modification within 24K hours since delivery or 24K hours since last overhaul but the Table specifically stated whicheve